Controlling silver release from antibacterial surface coatings on stainless steel for biofouling control

This study focuses on the in-situ nucleation of silver nanoparticles (AgNPs) on stainless steel (SS) to provide a localized antibacterial action for biofouling control during space missions. Since AgNPs rapidly dissolve in water, partial passivation of AgNPs was provided to slow down silver release and extend the lifetime of the antibacterial coating. Two different passivation approaches, based on the formation of low solubility silver sulfide (Ag₂S) or silver bromide (AgBr) shells, were compared to identify the optimal passivation for biofouling control. Highest bacterial inactivation (up to 75%) occurred with sulfidized AgNPs as opposed to bromidized (up to 50%) NPs. The optimal passivation treatment for biofouling control was found at 10^-5 M Na₂S (for Ag₂S) and 10^-3 M NaBr (for AgBr) concentrations. Scanning Electron Microscopy (SEM) analyses confirmed the presence of AgNPs on AgBr and Ag₂S-coated samples. Further investigation revealed that compared to pristine AgNPs, Ag release from both sulfidized and bromidized NPs was significantly lower (16% vs 6% or less). Overall, both sulfidized and bromidized AgNPs were effective at controlling biofilm formation; however, sulfidized NPs exhibited the maximum antibacterial activity, making it the preferable passivation strategy for AgNPs on SS surfaces.